See three posts back- polypro is known for its smell trapping properties. I am not sure about it relative to vinyl. I was just guessing, which is why I said "I suspect" polypro>vinyl. It doubt it is any less than vinyl, which already holds/releases too much residual flavor, and plastic taste, for me.
A good sequence for correcting foam is:
Set the proper psi for the temp and vols of co2.
Check faucet/tower/shank temps and get them close to keg temps.
Start with at least the proper length of line. Add more if still foaming until the flow becomes an issue, or reduce length if no foam and flow is an issue.
Check all connections for possible cavitation/nucleation issues.
Decrease the serving temp and corresponding psi (and pour into a warmer glass, if you are one of those types).
Personally, I don't know why people go to all this trouble to have/fix short hose issues, especially if they are using vinyl tubing. Is there a short hose award I don't know about? If there is, the prize should be a Porsche.
I wouldn't mess around with any of this nonsense for normal beer pressures. I would just add a few more feet of accuflex bev-seal ultra barrier tubing. It is much smaller overall than vinyl and coils tightly, so 25ft shouldn't be a size issue. It also doesn't funk up the beer after long periods, or pick up flavors, so the longer length is better than a shorter length of vinyl.
The only thing I may try is some teflon rope/cord inserted into some larger barrier tubing (1/4", 3/8") to increase the surface area while still keeping the flow high and velocity low (another cause of foaming). Trying to serve soda and cider at ~30psi is problematic. Hopefully the SS Perlick flow control will be available soon.